1. Field of the Invention
This invention relates to a fitting assembly of the type intended to be used in combination with a conduit through which high pressure fluiid passes and which incorporates a fitting body having a base and a plurality of segments spaced apart from one another and extending outwardly therefrom wherein a force applying means applies an external force to the plurality of segments creating a bending moment about a gripping portion on each of the segments and forcing the gripping segments to engage the outer surface of the conduit at the gripping portion and at a spaced apart free end of each segment from the gripping portion to provide a bending support surface which relieves stress on the conduit during vibration thereof at the point of gripping engagement between the gripping portion and the outer surface of the conduit.
2. Description of the Prior Art
An area of substantial technical and commercial importance has been the use of metal tubes or conduits, of different wall thickness, to contain fluid media such as liquid, gases, etc. for use in areas such as high pressure hydraulics, gas transmission systems, air conditioning systems and the like. Fittings for joining or connecting such tubing exist in a variety of forms but all must perform certain basic functions. These functions include the mechanically holding of the tubes or conduits together or the holding of a single tube in another structure. In addition, the aforementioned functions further include the providing of a leak proof seal for the liquid or gas contained within the conduit. Another important function of the type of fitting referred to is the resisting of bending fatigue which arises from the movement of the tube being held by the subject fitting. Also, a preferred fitting structure should provide or facilitate re-usability so that the fitting can be applied, removed and then reapplied again for additional usage. The subject preferred fitting should also be vibration resistant again, in order to resist the bending fatigue as set forth above.
One category of fittings existing in the prior art and attempting to overcome the aforementioned problems includes the use of a compression ring or ferrule. In this type of fitting, a compression ring or ferrule, which is a piece of hardened metal formed into a ring or cone-like structure, without being split, is forced onto the outer surface of a conduit to hold the conduit and to form a pressure seal. This fitting is not unitary and the basic functions of holding and sealing are performed by the compression ring. In some designs evident in the prior art, two rings are required such as is demonstrated in U.S. Pat. No. 4,304,422.
Another category includes the utilization of a split collet or split cone or ring design. In this prior art category of fittings a spilt collet squeezes upon a tube or the outer portion thereof with the tightening of a nut as demonstrated by certain fittings commercially available and manufactured by the Lenz Corporation.
Split jaws with a taper or with a tapered nut define yet another category of prior art fittings. In such type of fittings an "O" ring seal is used for the pressure seal in conjunction with a metal tube. A mechanical grip is provided by the split jaws either squeezing directly upon the tube or by the jaws squeezing an inserted split ring which is then squeezed upon the tube. This latter method is not unitary. For example, the use of a split ring as an intermediary in holding is disclosed and taught in U.S. Pat. No. 3,843,169 to Wise and also in British Patent No. 345,746 to Turner.
In the case of the split jaws squeezing directly upon the outer surface, the holding or gripping ability of the fitting is derived from the frictional contact of the inner surface of the fitting jaws and the outer surface of the tube. Thus, in the prior art of tapered jaw fittings, attempts were made to maximize the area of surface contact between the inner surface of the jaws and the outer surface of the tube. An example of this category of prior art fittings is disclosed in French Patent No. 2442392 to Forges. A number of devices which are not fittings per se also attempt to hold an object in frictional contact. Many of these devices may be considered clamps for holding drill bits, axial shafts and solid circular rods of various types. Some example of devices of these segmented jaw clamps include British Patent No. 1047869 to Ross and U.S. Pat. Nos. 4,095,914 to Thompson and 923,014 to Garretson.
It is important to recognize that there is a fundamental difference between devices designed to grab and hold solid metal shafts and fittings designed to grab and hold metal tubing. This difference is perhaps not so obvious when comparing split jaw fittings which utilize surface friction and split jaw clamps which also utilize surface friction. However, as will be seen in the present invention to be described in greater detail hereinafter, a new category of fittings of which the present invention is a part does not depend upon surface friction between jaws and the outer surface of the tube or conduit for holding. The difference, as demonstrated by the present invention, is truly dramatic and a fundamental difference from the aforementioned prior art fittings.
Using a tapered nut in combination with externally and internally threaded jaws is demonstrated in U.S. Pat. No. 2,383,692 to Smith. Smith attempts to improve holding power by having the internal threads "bite" into the external surface of the tube. A key point to note in the fitting design of Smith is that the internal thread extends over the entire interior surface area of the jaw right up to the end of the jaw. As will be seen, this renders the Smith design ineffective in reducing or eliminating bending fatigue.
A key point to note in the various segmented end fittings demonstrated in the prior art is that the outer surface of the segments thereof are almost entirely covered with threads. Generally, the outer surfaces of the segments are threaded from the distal end of the segment to a point near where the segment joins the main body or base of the fitting. This is true both in the case of Smith as set forth above and Forges, both previously referenced. The same may be said of the segmented clamping devices which are not fittings per se, such as demonstrated an taught in U.S. Pat. No. 1,659,268 to Hooley; Heyner, Swedish Patent No. 87205 and Habler, German Patent No. 7628297. The prior art has developed to a point where it appears natural to have as much as possible of the external surface of the segment or jaw covered with threads since a large number of force vectors, one at each thread surface, is produced in order to maximize the overall spread of gripping force and thereby increase the bite holding or gripping ability of the fitting. As will be seen hereinafter, this reasoning in the prior art was misdirected and the gripping ability can be vastly improved through the novel force distribution considerations demonstrated in the present invention.
An additional point to note in the Hooley patent as set forth above is that the conduit connector includes small ribs or studs on the internal jaw surface. Such ribs or studs are not suitable for fittings as such projections will interfere with the small clearance required between the O-ring seals and the tube surface for effective design and sealing.
Also present in the prior art is the demonstration of split jaws without tapered jaw or nut and without shaped or inclined jaw ends. Such a fitting design of this type is singularly demonstrated in U.S. Pat. No. 4,544,186 to Proni (inventor herein). The Proni structure is the only fitting design which operates on a purely radial displacement produced by a camming reactive force. In the Proni design force is exerted upon the threads on the outer surface of the jaws, causing the jaws to move radially inward. In one embodiment of the Proni structure the interior surfaces of the jaws possess a tip which is located at the distal end of the jaw segments. This jaw design is ineffective or less than efficient in resisting bending fatigue. The tip located at the end of the jaw is a stress riser, leading to premature failure under bending or vibration of the tube.
Further, in the Proni structure as in the design of other prior art split jaw fittings, no consideration is given to force concentration at specific locations along the segment or jaw external surface. In fact, in the Proni fitting design as in the clamp design of Heyner, previously referenced, the largest force is exerted upon the jaw thread surface closest to the camming action surface or shoulder; the second largest force on the second jaw thread surface, the third largest force on the third threaded surface, and so on. This method, as demonstrated, is less than totally effective in developing a clamping force since the bending moment of the closest thread surface is very small and as the distance of the subsequent thread surfaces from the shoulder or camming surface of the Proni fitting increased the force per thread decreases resulting in ineffective gripping. The only consideration given in the Proni design to a separation of threads from the camming surface is to increase the flexibility or bendability of the jaw segment itself. No consideration is given or implied to spatial force concentration or distribution.
It should be readily apparent, therefore, that in overcoming the problems present in the prior art the specific need is for a split jaw or segmented end fitting which provides excellent bending fatigue resistance while gripping and sealing high pressured fluid carrying conduits or tubes. In particular, a fitting design which can separate the functions of sealing, gripping and fatigue resistance by spatially separating the interior fitting structures performing the above functions is needed. To the knowledge of the inventor herein no such unitary fitting structure exists in the prior art.
To achieve the specific need a second specific need presents itself. This second need is for a spatially structured force upon the external surface of each jaw or segment. The spatial structure of this force must be such that the force is maximized at a specific range interval from the distal or free end of the jaw or segment. With such a spatially structured force appropriate movements and secondary bending moments can be generated. No unitary fittings of which the inventor herein is aware exist in the prior art which provide the spatially concentrated forces upon the outer surfaces of the segment within a selected range of intervals or distances from the free end of the segment.
Such spatial concentration of forces at specified range of distances upon the outer surface of the segments cannot be achieved by mere selection of thread design. Such a concentration is a fundamental insight requiring novel structural features as set forth hereinafter in the present invention.